Dietary fiber is dietary matter which increases fecal bulk. It is formed from those parts of plant material in the diet which are resistant to digestion by secretions in the human gastrointestinal tract. Chemically, total dietary fiber includes cellulose, hemicellulose, pectins, gums, lignin and mucelagenous material. These are basically the fibers that pass through the intestines but are not acted upon in the gastrointestinal tract.
Adequate fiber in the human diet has been shown to be important for various health reasons including the reduction of the risk of certain types of cancer. Dietary fiber is also important because it permits increasing the bulk of food intake without increasing calorie content.
Plant fiber is added to domestic animal feed. Animals such as cows and pigs and the like have the ability to obtain some nutritional value from this material. Of course, with animals, such as cows and pigs, there is little or no concern with gritty feel, color, and the like. The fibrous material requires little, if any, pretreatment to be acceptable for these purposes.
Seed hulls, stems, wood, bark and the like have been suggested as sources of lignins, hemicellulose and other related products. These chemicals are removed from the plant material by extraction processes which presumably leave fibrous material as a residue or by product. This resulting unextracted fibrous residue is frequently discarded or used in a paper process or fed to animals. Accordingly, the quality of the residual fiber is not a primary concern and there certainly is no reason in these processes to attempt to obtain a product suitable for human consumption.
For example, Wolf et al U.S. Pat. No. 2,709,699 discloses the alkaline extraction of hemicellulose from plant substances. The hemicelluloses are used as thickening agents, protective colloids and ingredients in coating compositions. This patent does not disclose the status of the resulting undigested, unextracted material or even if there is any resulting undigested fibrous material.
Gerrish et al U.S. Pat. No. 3,879,373 discusses extraction of pentosans from wheat bran. If any resulting fibrous product is obtained, it is not disclosed, nor is there any suggestion of the use of any of the resulting fibrous material.
Friese U.S. Pat. No. 3,970,712 discloses a four step process for hydrolizing oat husks to obtain D-(+)-xylose. The solid residue is described as a "foodstuff grade cellulose". But following the steps disclosed in this patent to ensure adequate recovery of xylose provides a cellulose which has a gritty mouth feel and poor water absorbancy. Since the disclosed process attempts to maximize xylose recovery, quality of the resulting residue is a secondary consideration at best. Further, the residue has an off color, gritty mouth feel and poor water absorbancy. The multiple steps required to obtain the residue is also prohibitively expensive.
Antrim U.S. Pat. No. 4,038,481 discloses the treatment of corn hulls to obtain various fractions. Again there is no disclosure that the remaining undigested material is suitable for use as dietary fiber.
Kickle et al U.S. Pat. No. 4,181,747 and Antrim U.S. Pat. No. 4,239,906 disclose obtaining cellulosic products from seed materials.
Dietary fiber for human consumption must have various physical properties to be commercially acceptable. These properties are of little or no concern when the fiber is used for animal consumption or is the by product of an extraction. Of course it must have a high concentration of dietary fiber. Otherwise the product would serve no purpose or would have to be added in such high concentrations as to be impractical. Since hemicellulose is dietary fiber, it is important not to remove this when forming dietary fiber. It is believed that the hemicellulose helps reduce serum cholesterol.
The texture and mouth feel of the dietary fiber is also very important. If dietary fiber has a gritty feel, it will tend to alter the texture or mouth feel of any product to which it is added. This limits the percentage of dietary fiber which can be added to a product.
Water absorbancy is also important and is related to texture. A fiber which has a high rate of water absorbancy can be easily mixed and dispersed in a dough product. This permits addition of higher concentrations of dietary fiber. Also, this permits formation of a product which has a better mouth feel. Water absorbancy also improves the shelf life of the finished product. Physiologically water absorption is important to provide a stool softening effect reducing transit time and increasing bulk.
Thompson, U.S. Pat. No. 4,599,240 discloses a process of obtaining fibrous material from hulls of legumes such as soybean hulls. This process uses a complex bleaching process using chlorine gas with subsequent basic digestion. The reference indicates that this process is not applicable on a practical basis to wood, stalk portions of plants, or the husk portions of various cereal grains.
Because of its ability to produce a relatively white, non-gritty fiber, wood is currently the primary source of dietary fiber supplements. Because food components must frequently be identified in product labels and wood products are not perceived as an appealing food product, it is preferable to use a source of dietary fiber other than wood. Further, dietary fiber obtained from wood is so unpalatible that it can be substituted for no more than about 15% of the flour in bread.
In finding an alternate source of dietary fiber there are two major problems--selecting suitable plant material, and selecting a suitable extraction method. Many different types of plant material have been suggested as sources of dietary fiber varying from wood, which is most commonly used to various seed plant materials including pea hulls, corn hulls, peanut hulls, oat hulls and stems and the like. Generally the softer plant materials such as pea hulls and corn hulls are considered better sources because they are easily processed. However, these materials fail to provide a dietary fiber comparable in color, texture and water absorbancy to wood derived dietary fiber.
Oat hulls would seem to be a particularly good source material for dietary fiber. Their cost is low and currently are primarily used in furfural production, as fillers in foundry molds and as abrasive cleaners. There are sufficient oat hulls produced to supply most of the current demand for dietary fiber. Further, there is a year round supply of oat hulls.
In spite of this, oat hulls have not provided a source of dietary fiber comparable to wood fiber. Prior Methods of obtaining dietary fiber from oat hulls are unsuitable for obtaining a white dietary fiber that is even comparable to currently marketed wood fibers. Oat hulls contain a high concentration of lignin which is difficult to remove. Lignin content decreases water absorption and provides an off color. Oat hulls contain silica spicules. These spicules are pointed formations of silica which are part of the oat hull. The silica reduces water absorption and significantly increases the gritty feel of the obtained fibers. For these reasons, in spite of the availability and cost, one of the most apparently unsuitable materials for obtaining a dietary fiber is the oat hull.